How to Vent a Vaulted Roof

Vaulted roofs need ventilation to prevent heat damage.

A vaulted roof offers open living space directly below the rafters because there are no horizontal ceiling joists. Although there is no separate attic to vent, air circulation is still necessary to prevent heat from building up between the underside of the roof deck and the interior drywall finish.

Vaulted Roof Elements

A vaulted roof features angled rafters that rest on wall plates and connect at the top to a ridge beam. The thickness of the roof depends on the dimensions of the lumber used to construct the rafters. For example, if the rafters are two-by-ten boards, each rafter cavity will be 10 inches deep. Since there is no other available space, the rafter cavities are used for both insulation and venting purposes.

Intake Vents

The bottom of each rafter cavity ends at the soffit, which is the horizontal plane that lies just beneath the roof’s overhang. The homeowner has two choices for installing soffit vents, which will serve as the intake vents for the roof. A solid soffit board, with individual soffit vents installed beneath every rafter cavity is permissible. It's often easier, however, to install a vented soffit that features a continuous, perforated vent. Either method will provide intake venting.

Rafter Vents

Sometimes called “rafter baffles,” rafter vents are long and shallow, and as wide as the rafter cavities. They install on the underside of the roof deck, between the rafters, and extend from the soffit all the way to the roof ridge. Use one rafter vent per rafter cavity. Once the rafter vents are in place, you can install batt or rigid foam insulation and then finish the vaulted ceiling with drywall.

Ridge Vents

The cool, dry air that enters the soffit must have a place to exit. In a vaulted roof, a ridge vent serves as the outtake or exhaust vent. A ridge vent features an open strip along the length of the ridge where the air that enters the soffit can escape. A thin, perforated vent — overlapped with ridge shingles — camouflages the ridge vent when viewed from the street. Even when the sun beats mercilessly on the roof, cool, fresh air enters the soffit vents and flows upward and out of the ridge vent. This cools the underside of the roof deck, removing heat and moisture that could otherwise damage the roof.

Venting Vaulted Trusses

Some vaulted roofs don't have individual rafters, but instead feature pre-engineered trusses. Vaulted roof trusses are slightly misleading because the degree of vault on the exterior of the roof is not the same as the degree of vault inside, which is substantially less. Although the ceiling still vaults, there is plenty of space between the drywall and the top chord of the roof truss. Venting a roof with vaulted trusses requires the installation of soffit vents and the addition of at least two gable vents, positioned as high as possible on the sidewalls, to allow fresh air from the soffit to escape.

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